Preheat oven to 400°F and prepare a 9-inch glass pie plate with cooking spray.

In a 10-inch skillet, cook ground beef and onion over medium heat for 8-10 minutes until browned, then drain any fat. Stir in salt, spread the mixture into the prepared pie plate, and sprinkle with cheese.

Whisk together the remaining ingredients in a medium bowl until blended, then pour the mixture over the beef and cheese in the pie plate.

Bake for 29-33 minutes, or until a knife inserted into the center comes out clean. Let the pie stand for 10 minutes before serving.